The subject matter disclosed herein relates to a system for controlling a bucket hoist. More specifically, a controller generates control signals to a pair of motor controllers which work cooperatively to control operation of the bucket hoist for improved digging operation of the bucket hoist.
As is known to those skilled in the art, a bucket hoist may be used to transfer bulk materials from one location to another. A typical cycle of a bucket hoist begins with a load handling member suspended above the material to be transferred. The load handling member is opened and lowered toward the material to be transferred. When the load handling member reaches the bulk material, it is closed. As the load handling member closes, it digs into the bulk material in order to at least partly fill the load handling member with the bulk material. The load handling member is raised and moved to a new location at which the bulk material is to be dispensed. The new location may be, for example, a conveyor or vehicle by which the material is transported to an industrial process or to another location. The load handling member is opened and the bulk material empties from it.
The load handling member on the bucket hoist is controlled by the rotation of two motors. The load handling member is also referred to as a bucket, a clam-shell, or a grapple, and the motors are sometimes referred to as a closing motor and a holding motor. Each motor causes a sheave to rotate, around which is wound and unwound a rope connected between the sheave and the load handling member. The ropes may also be referred to as the closing rope and the holding rope, corresponding to the closing motor and holding motor, respectively, by which they are controlled. The holding rope is operatively connected either to a fixed point or through a first sheave block located near the top of the load handling member. The closing rope is operatively connected to a second sheave block located below and movable with respect to the fixed point or first sheave block. In order for the load handling member to be raised and/or lowered, each of the motors must operate to raise and/or lower the first and second sheave blocks in tandem. In order for the load handling member to open and/or close, the motors are operated in a differential manner such that the distance between the first and second sheave block varies. As the distance increases, the load handling member opens and as the distance decreases, the load handling member closes.
Historically, bucket hoists have been operated such that the closing motor opens and/or closes the load handling member. The holding motor is held in position either via a brake or via closed loop control of the motor. To open the load handling member, the closing motor runs in a first direction. The second sheave block lowers with respect to the first sheave block, and each half of the load handling member pivots outward about the first sheave block, causing the lower portion of the load handling member to open. To close the load handling member, the closing motor runs in a second direction, opposite from the first direction. The second sheave block raises with respect to the first sheave block, and each half of the load handling member pivots inward about the first sheave block, causing the lower portion of the load handling member to close. The bottom end of each half of the load handling member may include a digging member, such as a blade or teeth configured to engage the bulk material. As the load handling member closes and as each half pivots together, the digging member travels in an arc, digging into the bulk material. When the two halves are fully closed, the bulk material which was scooped by each half is retained within the load handling member.
However, closing the bucket in this manner results in the load handling member being only partial filled. Skilled operators of bucket hoists have learned to run the holding motor to lower the load handling member as the closing motor is run to close the load handling member. The load handling member digs further into the bulk material and results in a greater fill of the load handling member. Nevertheless, such operation is subject to variation by the operator between runs and requires skill to both maximize the fill and alternately, to avoid lowering the load handling member too fat which may result in the load handling member beginning to tip to one side.
Thus, it would be desirable to provide an automated control system to provide a uniform fill of the load handling member between runs with increased efficiency from having a greater fill percentage of the load handling member during each run.